This application claims benefit of priority under 35USC xc2xa7119 to Japanese patent applications No. 2000-089356, filed on Mar. 28, 2000 and No. 2001-028187, filed on Feb. 5, 2001, the contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates generally to a system for measuring the thickness of a film. More specifically, the invention relates to an eddy current loss measuring sensor for measuring an eddy current loss due to an eddy current which is excited in a conductive film on the surface of a wafer by magnetizing a high frequency magnetic field, in a process for fabricating a semiconductor integrated circuit device, a thickness measuring system and method for non-contact-measuring the thickness of the conductive film on the basis of the measured eddy current loss, and a computer readable recorded medium in which a program for executing the method has been recorded.
2. Description of the Prior Art
A method for measuring the thickness of a conductive film using an eddy current is effective in a non-contact, non-destructive thickness measuring technique.
In a thickness measuring method using an eddy current, the distance between a coil (sensor) for generating a magnetic field and a conductive film has a great influence on the quantity of an eddy current loss in the conductive film. Therefore, it is important to precisely control the distance between the sensor and the conductive film.
FIG. 23 shows a data in an example of an experiment in which the quantity of an eddy current loss was measured as the variations in inductance and resistance of a sensor. It can also be understood from this figure that the inductance and resistance of the sensor vary in accordance with the distance between the sensor and the conductive film.
In order to reduce measurement errors due to such dependency on distance to improve measurement precision, the following techniques are proposed.
For example, as a first method, as shown in FIG. 23, there is a method for previously obtaining a correlation between the distance between a sensor and a conductive film and a measured value and for carrying out measurement at a plurality of points while varying the distance between the sensor and the conductive film, to carry out correction at the respective points of measurement using the above described correlation.
As a second method, as shown in FIG. 24, there is a method for measuring inductance Q by means of an impedance analyzer, when coils 103a and 103b for exciting an eddy current are provided on both sides of a conductive film serving as an object to be measured, so as to face each other via the conductive film, and connected in series.
However, according to the above described second measuring method, there is a disadvantage in that the system is complicated and large-scale.
In the first method for carrying out measurement at the plurality of points while varying the distance, the sensor or stage must be operated times of measurement, and a data processing must be every one of the points of measurement, so that it takes very much time to carry out the measurement. Therefore, there is a problem in that this method is of no practical use since it is unsuitable for a high-speed measurement, which is required in a mass production line, and for a real-time measurement in a thickness forming process.
On the other hand, as an attempt to localize a magnetic field, which is generated by a coil, at a point in order to enable to carry out a localized thickness measurement to improve measurement precision, there is only a method for inserting a core 110 of ferrite or a magnetic material into a coil 108 as shown in FIG. 25, in addition to a method for decreasing the diameter of the coil to enhance resolution.
As a sensor for measuring a displacement of a metal conductor, a sensor for localizing a magnetic field on a conductor is proposed. Referring to FIGS. 26A through 26D, an example thereof will be described below.
As shown in FIG. 26A, a displacement sensor comprises a receiving coil 112 wound onto a ferrite core 111, a high frequency exciting coil 113 wound onto the outside of the receiving coil 112, and an outer screening plate 114 of copper which is provided so as to cover the ferrite core 111 and the coils 112 and 113, and the top of which is open.
The high frequency exciting coil 113 is designed to receive a high frequency current to generate a magnetic field to excite an eddy current to a metal conductor C serving as an object to be measured. The receiving coil 112 is designed to receive a magnetic field having a magnetic flux density which is reduced by the eddy current produced by the metal conductor C.
The outer screening plate 114 comprises semi-cylindrical portions 114a and 114b which are arranged so as to face each other. Typically as shown in FIG. 26B, the semi-cylindrical portions have semi-circular bottom plate half-portions 114c and 114d, respectively. The right and left semi-cylindrical portions 114a and 114b are arranged so as to face each other via a minute clearance to form a radially extending insulating slit 115 between the bottom plate half-portions 114c and 114d as shown in the bottom drawing of FIG. 26C. Thus, the outer screening plate 114 comprises the right and left semi-cylindrical portions which are separated from each other by the insulating slit 115 to be insulated from each other. While the linear insulating slit has been described in this embodiment, a cross insulating slit may be formed.
If a high frequency exciting current is passed through the high frequency exciting coil 113, a high frequency magnetic field is produced to induce an eddy current in the right and left bottom plate half-portions 114c and 114d of the outer screening plate 114. Since this eddy current is generated in a direction in which the magnetic field is interrupted, a synthetic magnetic field of the magnetic field due to the exciting coil 113 and the magnetic field due to the eddy current in the respective bottom plate half-portions 114c and 114d has a small magnetic flux density in the respective bottom plate half-portions 114c and 114d, and a large magnetic flux density in the insulating slit 115. For that reason, as shown in FIG. 25D, an uneven high frequency magnetic field having a magnetic flux density of a maximum value Bmax in an insulating slit portion S0 is formed in a sensor head. Therefore, when the sensor head is arranged above the metal conductor C of a copper wire or the like as shown in FIG. 26A, if the conductor C is arranged directly below the insulating slit 115 of the outer screening plate 114, the electric flux density in a space occupied by the conductor C is maximum, and the screening effect of the outer screening plate 114 is weakest with respect to the alternating magnetic field induced by the eddy current of the conductor C. At this time, the influence of the conductor C on impedance of the receiving coil 112 of the sensor head is maximum.
Thus, the structure in which the linear or cross slit causes the magnetic flux to extend into the longitudinal region is effective in the examination of the displacement of an elongated body of a metal conductor or the like. However, this structure is insufficient for a localized thickness measurement since it is required to form a magnetic field serving as a stop.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide an eddy current loss measuring sensor capable of carrying out a localized thickness measurement, a thickness measuring system and method for rapidly and precisely measuring the thickness of a film, and a computer readable recorded medium in which a program for executing the method has been recorded.
According to a first aspect of the present invention, there is provided an eddy current loss measuring sensor comprising: an exciting/receiving coil for receiving a high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film which is an object to be measured, and for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field; a first magnetic permeable member inserted into the exciting/receiving coil to serve as a core, the first magnetic permeable member being formed of a first magnetic permeable material; and a second magnetic permeable member provided so as to surround the first permeable member and the exciting/receiving coil, the second magnetic permeable member being formed of a second magnetic permeable material and having a surface facing the conductive film, the surface having an opening so that a region of at least a part of the exciting/receiving coil is exposed.
The magnetic flux generated by an exciting/receiving coil form a magnetic circuit wherein the magnetic flux leaks out only from an opening to the outside via a first magnetic permeable member to draw a curve to return to the first magnetic permeable member via a second magnetic permeable member. The second magnetic permeable member prevents the magnetic flux from leaking out to the outside of the sensor. Thus, the curve can be sharp. Therefore, if an eddy current loss measuring sensor is arranged in the vicinity of a conductive film so as to face the conductive film so that the vertex of the curve is arranged in the conductive film, it is possible to excite an eddy current only in a very small region. Thus, it is possible to measure the quantity of an eddy current loss in a localized region, so that there is provided a high-accuracy eddy current loss measuring sensor which does not destroy an object to be measured and which does not prevent a process for depositing, etching or polishing a conductive film.
According to a second aspect of the invention, there is provided an eddy current loss measuring sensor comprising: an eddy current exciting coil for receiving a high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film serving as an object to be measured; a receiving coil, provided so as to be wound by the eddy current exciting coil in the eddy current exciting coil, for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field; a first magnetic permeable member inserted into the receiving coil to serve as a core; and a second magnetic permeable member provided so as to surround the first permeable member, the receiving coil and the eddy current exciting coil, the first magnetic permeable member being formed of a first magnetic permeable material, the second magnetic permeable member being formed of a second magnetic permeable material, and the second magnetic permeable member having a surface facing the conductive film, the surface having an opening so that a region of at least a part of the receiving coil is exposed.
If an eddy current exciting coil and a receiving coil are thus provided, there is provided an eddy current loss measuring sensor having a more excellent resolution.
The distance between the opening and the first magnetic permeable member may be adjusted so that a magnetic flux only leaks into a localized region of the conductive film.
In the above mentioned eddy current loss measuring sensor, the surface portion of the opening, or the surface portion of the opening and the surface portion of a region near the opening may advantageously be formed of a third magnetic permeable material having a higher magnetic permeability than that of the second magnetic permeable material. Thus, the magnetic flux leaking out of the opening can be localized in a further localized region.
The first through third magnetic permeable materials may preferably include an electric insulating material. This electric insulating material preferably includes ferrite.
According to a third aspect of the invention, there is provided a thickness measuring system comprising: an eddy current loss measuring sensor for receiving a high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film serving as an object to be measured, and for outputting the high frequency current which is influenced by an eddy current loss caused by the eddy current; an eddy current loss measuring part for detecting the high frequency current, which is outputted from the eddy current loss measuring sensor, to measure the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current to output the measured variation as data indicative of the magnitude of the eddy current loss; a distance measuring part for measuring the distance between the conductive film and the eddy current loss measuring sensor; and a thickness operation part for calculating the thickness of the conductive film on the basis of the measured result of the eddy current loss measuring part and the measured result of the distance measuring part.
The distance measuring part measures the distance between the conductive film and the eddy current loss measuring sensor, and the thickness operation part calculates the thickness of the conductive film on the basis of the measured distance and the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current. Thus, it is possible to reduce measurement errors depending on the distance, so that there is provided a noncontact, non-destructive thickness measuring system capable of precisely measuring the thickness.
The frequency of the high frequency current is preferably in the range from approximately 1 MHz through approximately 10 MHz.
In the above-mentioned thickness measuring system, the eddy current loss measuring sensor may preferably comprise: an exciting/receiving coil for receiving the high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film which is an object to be measured, and for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field, to output the high frequency current which is influenced by an eddy current loss caused by the eddy current; a first magnetic permeable member inserted into the exciting/receiving coil to serve as a core, the first magnetic permeable member being formed of a first magnetic permeable material; and a second magnetic permeable member provided so as to surround the first permeable member and the exciting/receiving coil, the second magnetic permeable member being formed of a second magnetic permeable material.
Alternatively, in the above-mentioned thickness measuring system, the eddy current loss measuring sensor may comprise:
an eddy current exciting coil for receiving the high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film serving as an object to be measured; a receiving coil, provided so as to be wound by the eddy current exciting coil in the eddy current exciting coil, for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field, to output the high frequency current which is influenced by an eddy current loss caused by the eddy current; a first magnetic permeable member inserted into the receiving coil to serve as a core; and a second magnetic permeable member provided so as to surround the first permeable member, the receiving coil and the eddy current exciting coil, the first magnetic permeable member being formed of a first magnetic permeable material, and the second magnetic permeable member being formed of a second magnetic permeable material.
The second magnetic permeable member may preferably have a surface facing the conductive film, the surface having an opening so that a region of at least a part of the exciting/receiving coil or the receiving coil is exposed.
If the opening is formed in the second magnetic permeable member, it is possible to locally measure the thickness of the conductive film. Thus, even in the case of a conductive film having a great dispersion of thickness, such as a conductive film formed on a substrate on which a pattern has been formed, it is possible to precisely measure the thickness of the conductive film. This is particularly advantageous to the monitoring of the thickness in parallel to a deposition process. In addition, it is possible to manage the thickness in various systems, such as CMP and plating systems.
The distance between the opening and the first magnetic permeable member may preferably be adjusted so that a magnetic flux only leaks into a localized region of the conductive film.
Furthermore, the surface portion of the opening, or the surface portion of the opening and the surface portion of a region near the opening may advantageously be formed of a third magnetic permeable material having a higher magnetic permeability that that of the second magnetic permeable material. Thus, the magnetic flux leaking out of the opening can be localized in a further localized region.
In the eddy current loss measuring sensor of the thickness measuring system, the first through third magnetic permeable materials preferably include an electric insulating material. This electric insulating material preferably includes ferrite.
The thickness measuring system may preferably further comprise: a memory for storing therein a measuring data indicative of a correlation between the distance between the eddy current loss measuring sensor and the conductive film, the frequency of the high frequency current, the thickness of the conductive film, the specific resistance of the conductive film, and the variation in impedance of the eddy current loss measuring sensor, or a correlation between the distance, the frequency, the thickness and the specific resistance, and the variation in current value of the high frequency current, or a correlation between the distance, the frequency, the thickness, the specific resistance, and the variation in phase of the high frequency current, wherein the thickness operation part calculates the thickness of the conductive film by comparing the measured variation in impedance of the eddy current loss measuring sensor, the measured variation in current value of the high frequency current or the measured variation in phase of the high frequency current with the measuring data.
The thickness measuring system may advantageously further comprises: a stage for supporting thereon a substrate on which the conductive film is deposited; and a control part for controlling a relative positional relationship between the stage and the eddy current loss measuring sensor on the basis of the measured result of the distance measuring part.
Using the control part, it is possible to hold a substantially constant distance between the stage and the eddy current loss measuring sensor on the basis of the measured results of the distance measuring system.
It is preferable that the control part moves the eddy current loss measuring sensor to a region which is not influenced by the eddy current, prior to the excitation of the eddy current into the conductive film, the eddy current loss measuring part measures the impedance of the eddy current measuring sensor, the current value of the high frequency current or the phase of the high frequency current, which are measured in the region which is not influenced by the eddy current, as a measuring reference value; and the thickness operation part corrects the calculated thickness value on the basis of the measuring reference value.
If a correction process is carried out, it is possible to suitably correct measurement errors due to external or internal factors.
In the thickness measuring system, a reference conductive film serving as a reference of measurement may be previously prepared in the region which is not influenced by the eddy current, the control part may move the eddy current loss measuring sensor to the region in which the reference conductive film has been prepared, prior to the excitation of the eddy current into the conductive film serving as the object to be measured, and the eddy current loss measuring part may measure the eddy current loss using the impedance of an eddy current loss measuring sensor, the current value of the high frequency current or the phase of the high frequency current, which are measured in the region in which the reference conductive film has been formed, as a measurement reference value.
It is preferable that the reference conductive film may be a plurality of the reference conductive film each of which is formed of conductive material having conductivity different from each other and formed in thickness different from each other, the eddy current loss measuring part may measure a plurality of the measurement reference values, and the thickness operation part may correct the calculated thickness on the basis of the plurality of the measurement reference values.
It is preferable that the thickness measuring system further comprises; stage moving part for moving the stage; and a sensor moving part for moving the eddy current loss measuring sensor, wherein the control part controls the stage moving part and the sensor moving part so that the eddy current loss measuring sensor scans on the conductive film while holding a substantially constant distance between the eddy current loss measuring sensor and the conductive film, in parallel to a deposition, etching or polishing process for the conductive film.
If the control part cause the eddy current loss measuring sensor to scan, it is possible to rapidly measure the thickness.
The thickness measuring system may further comprises a stage moving part for moving the stage and a sensor moving part for moving the eddy current loss measuring sensor, and the control part may control the stage moving part so that the eddy current loss measuring sensor scans on the conductive film in parallel to a deposition, etching or polishing process for the conductive film, and the thickness operation part may receive the measured result of the distance measuring part to correct the calculated thickness value.
If the calculated thickness value is corrected on the basis of the measured results of the distance measuring part, it is not required to hold the constant distance during measurement. Thus, the eddy current loss measuring sensor can rapidly scan on the conductive film in parallel to the deposition process.
The eddy current loss measuring sensor may include an exciting/receiving air-cored coil for receiving the high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film which is an object to be measured, and for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field, to output the high frequency current which is influenced by an eddy current loss caused by the eddy current, and the distance measuring part may include a laser displacement sensor provided above the air-cored coil for emitting a laser beam to cause the laser beam to be incident on the surface of the conductive film via an air-core of the air-cored coil and for receiving light via the air-core, the light being reflected on the conductive film.
Alternatively, the eddy current loss measuring sensor may include an eddy current exciting coil for receiving the high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film which is an object to be measured, and an air-coiled receiving coil, provided so as to be wound by the eddy current exciting coil in the eddy current exciting coil, for receiving a synthetic magnetic field of a magnetic field generated by the eddy current and the high frequency magnetic field, to output the high frequency current which is influenced by an eddy current loss caused by the eddy current, and the distance measuring part may include a laser displacement sensor which is provided above the receiving coil for emitting a laser beam to cause the laser beam to be incident on the surface of the conductive film via an air-core of the receiving coil and for receiving light via the air-core, the light being reflected on the conductive film.
The laser displacement sensor causes the surface of the conductive film to be irradiated with laser beams via the air-core of the air-cored coil or of the receiving coil, and receives the reflected light via the air-core, so that the intersection between the center line of the air-core and the surface of the conductive film, or a region near the intersection is irradiated with the laser beams. Therefore, the distance between the eddy current loss measuring sensor and the conductive film can be directly measured. Thus, the measurement of the distance and the measurement of the eddy current loss can be simultaneously carried out in parallel.
The thickness measuring system may further comprise a distance measurement error correcting part for driving the laser displacement sensor to measure the distance prior to the measurement of the thickness of the conductive film, and for correcting a measurement error of the measured result, and the control part may control the stage moving part and the sensor moving part on the basis of the measured distance, which is corrected by the distance measurement error correcting part, so that the eddy current loss measuring sensor scans on the conductive film while holding a substantially constant distance between the eddy current loss measuring sensor and the conductive film. Alternatively, in place of the fact that the eddy current loss measuring sensor scans on the conductive film while holding a substantially constant distance between the eddy current loss measuring sensor and the conductive film, the thickness operation part may correct the calculated thickness value on the basis of the measured distance corrected by the distance measurement error correcting part.
Since the distance measurement error correcting part corrects the measurement errors of the distance before the thickness is measured, the distance measurement precision can also be improved with a small number of measuring points with respect to a conductive film which is formed on an LSI pattern to have a great variation in reflectance and/or which has a great roughness.
In the above mentioned thickness measuring system it is advantageous that the distance measuring part may include a capacitance type displacement sensor having an electrode provided in the vicinity of the eddy current loss measuring sensor for measuring the distance on the basis of an electrostatic capacity between the electrode and the conductive film.
Since the capacitance displacement sensor is not influenced by the reflectance of light and/or roughness on the surface of the conductive film, the distance measuring part can precisely measure the distance between the eddy current loss measuring sensor and the conductive film. In this case, the potential of the conductive film is held at the ground potential. This is realized by grounding a side of a substrate on which the conductive film is formed or by grounding the top surface or the reverse surface of a region, which has no influence on the measurement of the thickness, of the region of the conductive film.
The measuring electrode may preferably be provided so that the bottom face of the measuring electrode is substantially arranged on the same plane of the bottom face of the eddy current loss measuring sensor. Thus, it is possible to directly measure the above described distance.
In addition, the measuring electrode may preferably be a thin film electrode made of a high resistance material. Thus, it is possible to reduce the possibility of generating an eddy current in the measuring electrode itself.
Moreover, if the measuring electrode comprises a plurality of electrode pieces, it is possible to further reduce the possibility of generating an eddy current in the measuring electrode itself.
Furthermore, it is advantageous that the measuring electrode may have a ring shape surrounding the eddy current loss measuring sensor, the external diameter thereof may be substantially the same as the diameter of a region in which an eddy current loss is generated by the eddy current excited in the conductive film by the eddy current loss measuring sensor, and the internal diameter thereof may be selected so that the eddy current excited in the measuring electrode by the eddy current loss measuring sensor is small so as to be capable of being ignored in measurement and so that the measuring electrode has a surface area so as to be capable of measuring the electrostatic capacity between the measuring electrode and the conductive film. Thus, it is possible to further avoid generating the eddy current.
In the thickness measuring system, the stage may preferably be formed of an insulating material or a material having conductivity so that only a small quantity of eddy current capable of being ignored is generated in measurement, even in receiving the high frequency magnetic field. Thus, since the eddy current loss generated in the stage is greatly suppressed, it is possible to further enhance the measurement precision.
The thickness measuring system may advantageously further comprises a frequency control part for controlling the frequency of the high frequency current so that the high frequency current has a frequency according to the thickness of the conductive film.
The permeating depth of an eddy current into the conductive film varies in accordance with the frequency of a magnetic field exciting the eddy current. Therefore, if the frequency of the high frequency current is flexibly adjusted in accordance with the estimated value of the thickness of the conductive film, it is possible to enhance the resolution of the system.
In addition, if the thickness measuring system is used in parallel to a deposition process for the conductive film, the frequency of the high frequency current can appropriately be adjusted in accordance with a variation of the thickness. Thus, it is possible to more rapidly scan on the surface of the substrate, and it is possible to precisely monitor the thickness in real time.
If the conductive film is deposited above a circuit pattern including a conductive material or an underlying conductive film, the thickness operation part of the thickness measuring system may previously calculate a thickness value of the circuit pattern or the underlying conductive film as an underlayer thickness value, a total thickness value of the underlayer thickness value and the thickness value of the conductive film during or after the deposition of the conductive film, and substrate the underlayer thickness value from the calculated total thickness value.
Thus, since a previously calculated underlayer thickness value is subtracted from a total thickness value, even if the conductive film serving as an object to be measured is deposited above a circuit pattern or an underlying conductive film, it is possible to precisely measure only the thickness values.
The above mentioned thickness measuring system may further comprise a plurality of the eddy current loss measuring sensors.
If a plurality of eddy current loss measuring sensors are simultaneously controlled to scan on the surface of the conductive film on the substrate, it is possible to rapidly measure the thickness distribution.
In the thickness measuring system, the eddy current loss measuring sensor may be provided so as to face a surface on which the conductive film serving as the object to be measured is deposited, etched or polished, or so as to face a substrate surface on the opposite side to a surface on which the conductive film serving as the object to be measured is deposited, etched or polished, or so as to face both of a surface on which the conductive film serving as the object to be measured is deposited and a substrate surface on the opposite side to the surface on which the conductive film serving as the object to be measured is deposited, etched or polished.
If the eddy current loss measuring sensor is provided so as to face a substrate surface on the opposite side to a surface on which the conductive film serving as an object to be measured is deposited, etched or polished, it is possible to eliminate the possibility of preventing the deposition, etching or polishing of the conductive film serving as the object to be measured, in the deposition, etching or polishing process, and it is possible to measure the thickness while the eddy current loss measuring sensor contacts the substrate surface. Moreover, it is not required to scan while avoiding contacting a polishing tool in the CMP process. Thus, there is provided a thickness measuring system which can greatly reduce constraints on measurement and which has excellent degree of freedom of design and throughput in measurement.
According to a fourth aspect of the present invention, there is provided a thickness measuring method using a thickness measuring system having an eddy current loss measuring sensor for exciting a high frequency magnetic field to excite an eddy current in a conductive film, which is an object to be measured, and for detecting an eddy current loss caused by the eddy current, and a distance measuring part, the method comprising: a distance measuring step of measuring the distance between the eddy current loss measuring sensor and the conductive film by means of the distance measuring part; an eddy current loss measuring step of supplying a high frequency current to the eddy current loss measuring sensor to excite the high frequency magnetic field to excite an eddy current in the conductive film to measure the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current on the basis of the high frequency current outputted from the eddy current loss measuring sensor; and a thickness calculating step of calculating the thickness of the conductive film on the basis of the variation in impedance and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in current value of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in phase of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film.
According to the thickness measuring method, the thickness of the conductive film is calculated on the basis of the variation in impedance and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in current value of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in phase of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film, so that it is possible realize a non-contact, non-destructive, precise thickness measurement.
The thickness calculating step may includes: a first calculating step of calculating the thickness of the conductive film on the basis of the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current; and a first correcting step of correcting the thickness value, the thickness value being obtained at the first calculating step, on the basis of the relationship between the distance and the impedance, or the relationship between the distance and the current value of the high frequency current, or the relationship between the distance and the phase of the high frequency current.
It is preferable that the distance measuring part includes an optical displacement sensor and the thickness measuring system further comprises a distance measurement error correcting step of driving the optical displacement sensor to measure the distance prior to the measurement of the thickness of the conductive film and of correcting a measurement error of the measure result, the thickness calculating step including a step of correcting the calculated thickness value on the basis of the measured distance corrected at the distance measurement error correcting step.
Since a distance measurement error correcting step is further provided, it is also possible to improve the distance measurement precision with a small number of measuring points with respect to a conductive film which is formed on an LSI pattern to have a great variation in reflectance and/or a conductive film which has a great roughness on the surface.
It is advantageous that if the eddy current measuring sensor includes an air-cored coil, and distance measuring part includes a laser displacement laser, provided above the air-cored coil, for emitting a laser beam to cause the laser beam to be incident on the surface of the conductive film via an air-core of the air-cored coil and for receiving light via the air-core, the light being reflected on the surface of the conductive film, the distance measuring step and the eddy current loss measuring step are simultaneously carried out in parallel.
The laser displacement sensor causes the surface of the conductive film to be irradiated with laser beams via the air-core of the air-cored coil, and receives the reflected light via the air-core, so that the intersection between the center line of the air-core and the surface of the conductive film, or a region near the intersection is irradiated with the laser beams. Therefore, the distance between the eddy current loss measuring sensor and the conductive film can be directly measured. Thus, it is possible to enhance the distance measurement precision.
In addition, since the distance measuring step and the eddy current loss measuring step are simultaneously carried out in parallel, it is possible to greatly improve the throughput in the measurement of the thickness.
In the thickness measuring method of the present invention, it is preferable that if the distance measuring part of the thickness measuring system includes a capacitance type displacement sensor having a measuring electrode provided in the vicinity of the eddy current loss measuring sensor for measuring the distance on the basis of an electrostatic capacity between the measuring electrode and the conductive film, the distance measuring step and the eddy current loss measuring step are simultaneously carried out in parallel.
According to the measuring method, the capacitance displacement sensor which is not influenced by the reflectance of light and roughness on the surface of the conductive film is used, so that it is possible to precisely measure the above described distance.
The thickness measuring method may further comprise a reference value measuring step of, prior to the eddy current loss measuring step, supplying the high frequency current to the eddy current loss measuring sensor in a region which is not influenced by the eddy current loss and of measuring an impedance of the eddy current loss measuring sensor, a current value of the high frequency current or a phase of the high frequency current on the basis of the high frequency current outputted from the eddy current loss measuring sensor as a measuring reference value, and the thickness calculating step including a second correcting step of correcting the value of the thickness on the basis of the measuring reference value, the value of the thickness being obtained at the first calculating step.
A reference value measuring step for obtaining a measurement reference value in a region which is not influenced by the eddy current loss is further provided, and the thickness measuring step includes a first correcting step of correcting the calculated thickness value on the basis of the measurement reference, so that it is possible to prevent the drift of the measured value due to the fluctuation of the system and so fourth.
When a reference conductive film is previously prepared in the region which is not influenced by the eddy current, the reference conductive film serving as a reference of measurement and having a predetermined thickness, the reference value measuring step may preferably be a step of measuring the impedance of the eddy current loss measuring sensor, the current value of the high frequency current or the phase of the high frequency current as the measuring reference value, the impedance, the current value and the phase being measured in a region in which the reference conductive film is deposited.
Furthermore, if a plurality of the reference conductive film are previously prepared and if each of the reference conductive film are formed of conductive material having conductivity different from each other and formed in thickness different from each other, the reference value measuring step may be a step of measuring a plurality of the measurement reference values.
If the thickness measuring system further comprises a stage for supporting thereon a substrate on which the conductive film is deposited, the eddy current loss measuring step may preferably include a step of controlling a relative positional relationship between the stage and the eddy current loss measuring sensor so that the distance is substantially constant on the basis of the measured result at the distance measuring step. In addition, in place of the step of controlling a relative positional relationship so that the distance is substantially constant, the thickness measuring step may further include a second correcting step of correcting the thickness value, which is obtained at the first calculating step, on the basis of the relationship between the distance and the impedance, the relationship between the distance and the current value of the high frequency current or the relationship between the distance and the phase of the high frequency current.
If the thickness measuring system is used to a depositing process, an etching process or a polishing process for the conductivity film, it is advantageous that the thickness measuring method may advantageously be carried out in parallel to the deposition, etching or polishing step of the conductive film.
In addition, if the thickness measuring system is used to a process for a deposition, etching or polishing of the conductive film, the thickness measuring method may preferably comprise a step of controlling the frequency of the high frequency current.
Furthermore, if the conductive film is deposited above a circuit pattern including a conductive material or an underlying conductive film, the thickness measuring method may preferably include a step of previously calculating a thickness value of the circuit pattern or the underlying conductive film as an underlayer thickness value, a step of calculating a total thickness value of the underlayer thickness value and the thickness value of the conductive film during or after the deposition of the conductive film, and a step of subtracting the underlayer thickness value from the calculated total thickness value.
According to a fifth aspect of the present invention, there is provided a computer readable recorded medium for use in a thickness measuring system comprising an eddy current loss measuring sensor for exciting a high frequency magnetic field to excite an eddy current in a conductive film which is an object to be measured and for detecting an eddy current loss caused by the eddy current, a distance measuring part and a computer, the computer readable recorded medium including a program recorded therein for causing the computer to execute a thickness measuring method comprising: a distance measuring step of measuring the distance between the eddy current loss measuring sensor and the conductive film by means of the distance measuring part; an eddy current exciting step of supplying a high frequency current to the eddy current loss measuring sensor to excite the high frequency magnetic field to excite an eddy current in the conductive film; an eddy current loss measuring step of measuring the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current on the basis of the high frequency current outputted from the eddy current loss measuring sensor; and a thickness calculating step of calculating the thickness of the conductive film on the basis of the variation in impedance and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in current value of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film, or the variation in phase of the high frequency current and the distance between the eddy current loss measuring sensor and the conductive film.
According to the fifth aspect of the present invention, it is possible to precisely and rapidly measure the conductive film using a thickness measuring system comprising an eddy current measuring sensor, a distance measuring part and a general purpose computer.
In the above mentioned thickness measuring method, it is advantageous that the distance measuring step and the eddy current loss measuring step may be simultaneously carried out in parallel.
The thickness calculating step of the thickness measuring method may preferably include: a first calculating step of calculating the thickness of the conductive film on the basis of the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current; and a first correcting step of correcting the thickness value, the thickness value being obtained in the first calculating step, on the basis of the relationship between the distance and the impedance, or the relationship between the distance and the current value of the high frequency current, or the relationship between the distance and the phase of the high frequency current.
Furthermore, the thickness measuring method may preferably further comprise a distance measurement error correcting step of measuring the distance prior to the measurement of the thickness of the conductive film and of correcting a measurement error of the measured result, and the thickness calculating step includes a second correcting step of correcting the calculated thickness value on the basis of the measured distance corrected in the distance measurement error correcting step.